The present art of drilling pilot holes for fixating a bone plate relies totally on the surgeon's skill to accurately align and space screw pilot holes using a pneumatic power drill. The procedure is often complicated by the presence of body tissue, blood, and other body fluids in the operating field.
A bone plate is a device used in orthopedic surgery to secure and stabilize a very severe fracture. The plate is screwed into place over the fracture and the broken bones are thereby held together. A portion of the load applied to the bone is supported by the plate during the healing process. An example of one type of bone plate is shown in FIG. 2. Several screws are used to secure the plate to the bone segments. Different styles and lengths of these plates are used, depending on the type and location of the fracture.
The kind of fracture fixation involving the use of a bone plate is called "open reduction" and requires a surgical incision. Bone plates are used for very severe fractures, when fast healing is needed, or for very traumatized fractures where tissure damage already exists and there is no additional risk in surgery. Bone plates would probably not be used on the more simple transverse and oblique fractures. A cast would then provide the necessary stabilization.
If a bone plate is to be used, screw pilot holes are drilled into the bone. A pneumatic drill is usually employed to make these pilot holes for the screws, usually relying on the surgeon's skill to accurately align and space the holes. The operating site is not ideal for accurately positioning bone screws. In most cases, the body tissues are not completely cleared from the bone and the area is covered with blood and other body fluids.
A major problem in fracture fixation is to obtain accurate alignment of the pilot holes normal to the surface of the bone. In many cases, a surgeon will have difficulty in aligning the holes, and consequently the bone plate will not be securely attached to the bone. Misaligned screws can cause stress concentrations in the plate and perhaps cause splintering of the bone. Uneven stress distributions in the screws can be created by poor spacing of the pilot holes. Fracturing of the plate and screws, as well as fretting corrosion are not uncommon. There is a need for a drill guide with a clamping mechanism that would aid the surgeon in aligning and spacing the pilot holes.
There are currently several types of drill guides available for surgical use. All of these guides are hand-held, and in most cases, each hole is drilled independently of the next. None of the prior art drill guides is fixed to the bone, thus allowing tilting and slipping during the drilling procedure. Quite often the bone plate is used as a drill guide. In such cases it is possible that during drilling the bone plate could be nicked or marred. Any damage to the bone plate increases the possibility of corrosion.
Corrosion is an important problem to be considered in any implant procedure. If an implant is not made of a biocompatible material, corrosion and subsequent tissue inflammation is the result. In the body environment the galvanic reaction between two dissimilar metals is enhanced. For example, problems could occur if a titanium alloy plate is secured with stainless steel screws. Evidence of corrosion has also been witnessed when the screwdriver and the screws are not of the same alloy. It is thought that metallic particles from the screwdriver blade are deposited in the head of the screw. Because of the complexity of the corrosion problem, all efforts should be made to protect the screws from contact with dissimilar metals. This problem must be taken into consideration in the design of a drill guide/clamping system.
A preliminary search of the prior art revealed the following prior U.S. Pat. Nos. of interest:
McElveny, 3,244,170; PA1 McGuire, 3,835,849; PA1 Gil, 4,119,092; PA1 Cho, 4,257,411; PA1 Sayegh, 4,349,017.